Current driver circuitry for ferrite phase shifters

ABSTRACT

Current driver circuitry for magnetically saturable loads, such circuitry including feedback means for monitoring the time rate of change of flux in such load and disconnecting such circuitry when such rate of change of flux indicates that a saturation condition has been reached.

United States Patent 11 1 Auger Aug. 21, 1973 CURRENT DRIVER CIRCUITRYFOR [56] References Cited Inventor: Ernest g Billerica. Mass- 3,154,76310/1964 13611111611561 340/174 LA 3,175,098 3/1965 Grace 307/288 x [73]Assgnee' 33 Lexmgmn 3,446,984 5/1969 Shukla 340 174 LA 3,521,079 7/1970Kuck 307/270 x [22] Filed: July 31, 1972 211 App]. No.: 276,627 iiinw,fi t fykfisnflet 7 u Att0rney-Philip J. McFarland, Richard M. Shar-Related U.S. Appllcatlon Data k k et l I [63] Continuation of Ser. No.130,124, April 1, 1971, V V v abandoned- 57 ABSTRACT 521 vs. (:1343/854, 307/262, 307/270, current drive circuitry magneticallySan-"able 307/88 333/241, 343/754 loads, such circuitry includingfeedback means for 1511 1111. C1. H01q 3/26 Innnitnring the time ratechange flux in Such Field 61 Search 333/241; 307/101, and disconnectingsuch cnwiny when such 307/270, 88 314 343/100 SA 100 TD, change of fluxindicates that a saturation condition has 854; 340/174 LA been reached.

3 Claims, 4 Drawing Figures r 1: I I 4W l l 3 i I I 405 l -280 42s 1 l414$ 36 l V, I Z 1r- 538$ I 1 46s +v l l 1 FROM J 1 BEAM M G T I 260STEERING 1 COMPUTER, /5 l f 250 l l b /30 PAIENIEmuw ms 3.754.274

SHEET 1 BF 2 TRANSMITTER RECEIVER SYNCHRONIZER \2/ STEERING ,COMPUTERINVENTOR ERNEST R AUGE/P PAIENIEDMISZI I975 3.75427 SHEET 2 OF 2 FROMBEAM STEERING COMPUTER, l5

FROM BEAM STEERING COMPUTER/5 Zea/i 260 lNVENTOR ERNEST P. AUGER CURRENTDRIVER CIRCUITRY FOR FERRITE PHASE SHIFTERS This is a continuation ofapplication Ser. No. 130,124 filed Apr. 1, 1971 now abandoned.

BACKGROUND OF THE INVENTION This invention relates generally to currentdriver circuitry for magnetically saturable loads and more particularlyto current driver circuitry for ferrite phase shifter elements of thetype employed by phased array radar antennas.

As is known in the art, phased array radar antennas generally employmany thousands of ferrite phase shifter elements, such elements beingused to electronically steer the beam of an antenna to a desireddirection in response to electrical signals supplied by a beam steeringcomputer. As is also known in the art, each ferrite phase shifterelement normally is made up of a waveguide containing at least oneferrimagnetic toroid, each one of such toroids having at least onecurrent drive wire passing through the center thereof. The hysteresiscurve (sometimes referred to as the 8-H loop) associated with eachferrimagnetic toroid is substantially rectangular so that remanent fluxin the toroid may be made to be dependent on the time integral of apulse of voltage applied across a wire passing through the center ofsuch toroid. Either an analog or a digital signal may be used to achievea proper remanent state. With an analog approach one ferrimagnetictoroid is used for each phase shifter element, such toroid beinginitially reset to a reference remanent state by driving the toroid intosaturation of predetermined polarity, and secondly, set to a properremanent state by applying a pulse of voltage of proper time integralacross the current drive wire. With a digital approach, a number offerrimagnetic toroids are used for each phase shifter element, thenumbercorresponding to the number of bits in a binary word supplied bythe beam steering computer. Each one of such ferrimagnetic toroids isdriven into one of two remanent states by driving the toroid into one ofits two saturation conditions, the particular condition to which thetoroid is driven being in accordance with the binary state of theparticular control bit controlling such toroid. These conditions aregenerally called set" and reset." The proper saturation condition isachieved by passing current of sufficient level through a drive wire tosaturate the toroid, the direction of current flow through the drivewire being in accordance with the binary state of the control bit.

Therefore, for reason described above, it is necessary to drive theferrimagnetic toroids into saturation to properly control the amount ofphase shift required by the phase shift elements in directing the beamof the phased array antenna employing such elements regardless ofwhether the analog or digital approach is used. As is well known,however, when a ferrimagnetic toroid is driven into saturation, thepower dissipated in the current driver greatly increases because of thereduction in the inductive load impedance presented by the ferrimagnetictoroid. Such increases in power may cause the phase shifter element tobe heated excessively and, possibly, destroyed. Different techniqueshave been employed to prevent such power increases and, at the sametime, to reduce the capacity required of the attendant power supplyemployed by the antenna system. With a digital approach additionaltiming means may be provided for disconnecting the current driver fromthe toroid before thev undesirable large power condition occurs;however, this technique has been found lacking because of the variationin ferrite saturation time from toroid to toroid. Therefore, theduration of the pulse of voltage applied across the drive wire must bedesigned for worst case" conditions. Further, to permit a toroid to bedriven only from one saturation condition to the other, logic circuitrymay be provided to enable the control signal to be effected only whenthe sense of the control bit changes and to inhibit the control signalwhen the sense of the control bit does not change. This solution issubject to the reliability of the logic circuitry. In the analog schememeans may be provided to sense the magnitude of the current passingthrough the current drive wire so that, as the driver current approachesa predetermined maximum level, the driver current is reduced. Such anarrangement is described in Microwave Journal, Mar. 1967, LatchingFerrite Phase Shifter For Phased Ar rays, J. Frank, J. H. Kuck and C. H.Shipley. However, because all toroids are not identical, each .onerequires a different amount of current to actuate it; therefore, thepredetermined maximum level must be set high enough to account for thattoroid requiring the maximum amount of current to drive it intosaturation.

SUMMARY OF THE INVENTION It is, therefore, a primary object of theinvention to provide improved current drive circuitry for a magneticallysaturable load, such circuitry being designed to drive such load intosaturation with minimum power dissipation by the load.

It is another object of the invention to provide improved currentdriving circuitry for a magnetically saturable load, such circuitrybeing extremely reliable, and being adapted to prevent excessive currentfrom being drawn during operation.

These and other objects of the invention are achieved generally byproviding means for supplying sufficient current to a magneticallysaturable load to drive such load into saturation, and means for firstsensing the magnetization state of the load and then disconnecting theload from the current supplying means when such magnetization state isas desired. The invention takes advantage of the fact that the voltageinduced in a ferrimagnetic load is proportional to the time rate ofchange of magnetic flux density (i.e., dip/d!) generated by the currentsupplied to such a load, and that, in saturation, dqb/dt decreasessignificantly in magnitude as the load saturates. Therefore, in apreferred embodiment, the sensing means are provided to couple thevoltage developed across the load to the current driving means in such amanner that the magnitude of the voltage so coupled determines whetheror not the current driving means is connected to the load.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding ofthe invention reference is now made to the following description of theaccompanying drawings in which:

FIG. 1 is a simplified sketch of .a radar system using an array ofradiating elements, each one thereof being connected to a ferrite phaseshifter element which is driven by drive circuitry according to thisinvention to radiate a collimated beam of radio frequency energy and toreceive echo signals from targets illuminated by such radiated energy;

FIG. 2 is a cross-section of a ferrite phase shifter element of the typeshown in FIG. 1;

FIG. 3 is a schematic diagram of a current driver circuit embodying theinvention, such circuit being adapted to drive a ferrimagnetic toroidemployed by the phase shifter element shown. in FIG. 2; and,

FIG. 4 is a schematic diagram of an alternative embodiment of a currentdriver circuit for driving a phase shifter element of the type havingtwo current drive wires.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, it maybe seen that an antenna according to this invention includes a number ofphase shifter elements 11, each such element having associated therewitha current driving circuitry 13. The phase shifter elements 11 andassociated current driving circuitry 13 may be mounted in a conventionalmanner (not shown in detail) to form a space-fed planar array.Appropriate connections are made as indicated between each currentdriving circuitry 13 and the conductor for each ferrimagnetic toroid(shown in FIG. 2) of each phase shifter element 11 to drive each phaseshifter element 11 in accordance with digital control signals from abeam steering computer 15. As is known, such an arrangement permitsradio frequency energy from a feed born 17 to be collimated and directedin a beam as desired and echo signals returning to the individual phaseshifters of the antenna array to be focused on the feed horn 17. Thefeed horn 17 is connected in any convenient manner, as by waveguide (notnumbered) to a transmitter/receiver 19. The operation of thetransmitter/receiver 19 and the beam steering computer is controlled bya conventional synchronizer 21.

Each one of the phase shifter elements Ill includes a section ofwaveguide 23 with the ends (not numbered) thereof matched to free spaceby conventional matching devices 25, 25'. In the particular embodimentillustrated, each one of the phase shifter elements ll includes threeserially arranged ferrimagnetic toroids 26a, 26b, 26c (FIG. 2) tooperate in response to a three-bit control signal. Obviously, however,the number of toroids may be changed without departing from anyinventive concepts.

A different bit of a three-bit control signal is applied to a differentone of three identical current drivers l3a-c, which together make up thecurrent driving cir cuitry 13. A different one of the drivers 13a-c iscoupled to a different one of the ferrimagnetic toroids 26a-c viacurrent drive lines 28ac.

Referring now also to FIG. 3, an exemplary one of the current driversl3a-c (here current driver 13a), it may be seen that the beam steeringcomputer 15 transmits one bit of each one of the control signals tocurrent driver 13a via either line 42s or 42r. That is, a set signal istransmitted as a positive-going voltage square wave, i.e., a binaryzero, on line 42s and a reset" signal is transmitted as a negative-goingvoltage square wave, Le, a binary one," on line 42r. Exemplary currentdriver 13a is seen to comprise set circuitry 30s and reset circuitry3dr, such circuitry being connected to lines 42s and 42r, respectively,and being powered by a positive and negative power supply marked +V andv79 The reset circuitry 30r and set circuitry 305 are each comprised ofan input transistor 32r, 32s and an output transistor 3dr, 34s, theelectrodes of such input and output transistors being coupled, as shown,by a base resistor 36;, 36s, a bias resistor 38r, 38s and a feedbackresistor 41hr, 40s. The collector electrodes of output transistors 34s,34r are also connected together and to current drive line 28a, suchcurrent drive line passing through the approximate center offerrimagnetic toroid 26a, to ground as shown. Differentiatcrs, made upof capacitors 44s and 441* and resistors 46s and 46r as shown areconnected across the base and emitter electrodes of the inputtransistors 32:, 32s. To complete the reset circuitry Elllr, the emitterelectrode of input transistor 32r and the emitter electrode of outputtransistor 3dr are connected, as shown, to ground and to the negativepower supply, -V. Similarly for the set circuitry 30s, the emitterelectrodes of the input and the output transistors 32s, 34s areconnected to ground and to the positive power supply, +V.

In operation, when a binary zero is applied to line 42s, capacitor 44sand resistor 46s differentiate such signal in such a manner that theinput transistor 32s is immediately turned on." As the amplitude of suchdifferentiated pulse decreases the voltage across the base and emitterelectrode decreases until, absent any other effects, such voltagebecomes insufficient to maintain such transistor on. It will beobserved, however, that an effect does take place which latches inputtransistor 32s on, provided the ferrimagnetic toroid 26a is not in itsset" state. The reason for such latching is that when input transistor32s turns on during the initial portion of a set" signal, transistor 34salso turns on, thereby supplying current to the base electrode of inputtransistor 32s via feedback resistor 40s. Therefore, the inputtransistor 32s is latched on as long as the voltage across itsbase-emitter electrodes is greater than approximately +0.7 volts. Whenoutput transistor 34s turns on, a self-induced voltage is generated incurrent drive wire 280, the magnitude of such voltage being proportionalto the time rate of change of flux (i.e., drb/dt) through theferrimagnetic toroid 26a. Therefore, the magnitude of the voltage on thecollector electrode of output transistor 34s will be a function ofddw/dt. When ferrimagnetic toroid 26a saturates, dqb/dt is essentiallyzero. Therefore, as the ferrimagnetic toroid 26a approaches its setsaturation condition, the voltage on the collector electrode of outputtransistor 3% drops in magnitude and tends toward ground potential.Hence, the base-emitter electrode voltage of input transistor 32s dropsto less than 0.7 volts. Such input transistor therefore turns off,cutting output transistor 34.: off" so that current no longer flowsthrough drive wire 28a. If, however, the ferrimagnetic toroid 26a is inits set" saturation condition when a set signal appears, such a signalwould be differentiated to turn transistor 32.: on as before; suchtransistor would not be latched on" by output transistor 34s becauseddz/dt in the ferrimagnetic toroid 26 a would be zero and no currentcould be fed back to input transistor 32.: through feedback resistor40s. Reset circuitry 3dr operates in the same manner as set circuitry3%- except that the reset circuitry operates in response to anegative-going voltage square wave on line 42r and any current flowingthrough line 28a is in the opposite direction from the direction ofcurrent flow produced by set circuitry 30s.

Referring now to FIG. 4, another current driver I3'a embodying thefeatures of the invention is shown, such driver requiring that twocurrent drive lines pass through the approximate center of ferrimagnetictoroid 26a. Such a driver may be used when it is desirable to use apower supply of only one voltage polarity, here +V volts, and also whereit is desirable to have such driver turn on in response to binarysignals of one voltage polarity, here positive (i.e., the set circuitry30's and reset circuitry 30'r both respond to positive voltage pulsesapplied to lines 42's and 42'r). It is noted that the set circuitry 30'sand reset circuitry 30'r are similar in construction to each other and,with but one difference, to the set circuitry 30s shown in FIG. 3. Thedifference is that reset circuitry 30's and reset circuitry 30'r requirea blocking diode 50s and a blocking diode 50r respectively. The anode ofeach one of the blocking diodes 50s and 50r is connected, as shown, tothe collector electrode of input transistor 34's and 34r. Such diodesare necessary to eliminate any effect of mutual inductance betweencurrent drive wires 28'a and 28"a. Thus, when current flows into onesuch wire, say 28'a,

a voltage is induced in wire 28"a. In the absence of blocking diode 50r,input transistor 32r might thereby be turned on and latched on byfeedback from output transistor 34'r. Conversely, when current flowsthrough current drive wire 28"a, block diode 50s prevents inputtransistor 32's from being turned on and latched.

Numerous variations in the described embodiments, within the scope ofthe appended claims, will occur to those skilled in the art. Forexample, while a digital arrangement has been described, the currentdrivers can be used in an analog arrangement. Also, while aferrimagnetic toroid load was employed in the described embodiments,other magnetically saturable loads can be employed, such asFaraday-rotation phase shifter devices. These variations are merelyillustrative and hence it will be understood that the invention is notlimited in scope to the particular embodiment here shown, but only bythe appended claims.

What is claimed is:

1. In a phased array antenna assembly for collimating and directing abeam of electromagnetic energy by actuating, in accordance with controlsignals from a computer, each one of a plurality of magneticallysaturable phase shifters, each one of such phase shifters including atleast one magnetizable element having a first and a second saturationcondition determined by the direction of electric current through anenergizing coil, the improvement comprising:

a. separate first and second switching means, disposed in circuitbetween each energizing coil and the computer, for passing electriccurrent through each energizing coil in a direction determined by asignal from the computer; and

b. switching means control circuitry, disposed in operative relationshipto each one of the switching means and responsive to the saturationcondition of the associated magnetizable element when a signal isapplied by the computer, for permitting operation of the switching meansin operative relationship with such element only when the signal fromthe computer commands a change in the saturating condition of themagnetizable element.

2. In a phased array antenna system wherein an antenna beam iscollimated and directed in accordance with beam steering signalsproduced by a computer, the combination comprising:

a. a plurality of magnetically saturable phase shifter elements, aportion thereof being in a saturation condition; and

b. a plurality of means, each one thereof being coupled to a differentone of the plurality of magnetically saturable phase shifter elementsand responsive to the beam steering signals to establish a saturationcondition in selected ones of such elements by supplying current to theselected ones of such magnetically saturable phase shifter elementswhich are in an unsaturated condition and by inhibiting current frombeing supplied to the selected ones of such magnetically saturable phaseshifter elements which are in the saturation condition, each one of suchplurality of means comprising:

i. driving means having an input terminal in circuit with the computerand an output terminal in circuit with one of the plurality ofmagnetically saturable phase shifter elements, such driver means beingresponsive to the beam steering signals to vary the rate of change offlux in the magnetically saturable phase shifter element in circuittherewith in accordance with the initial state of the flux therein; and

disabling means, coupled between the input terminal and the outputterminal, and responsive to the rate of change of flux in suchmagnetically saturable phase shifter element to disable the drivingmeans when the rate of change of flux produced therein reaches asaturation level.

3. In a phased array antenna system wherein an antenna beam iscollimated and directed in accordance with beam steering signalsproduced by a computer, the combination comprising:

a. a plurality of magnetically saturable phase shifter elements; and,

b. a plurality of driver means, each one thereof being coupled to adifferent one of the plurality of magnetically saturable elements andhaving means responsive to the beam steering signals, to vary the rateof change of flux, and thereby establish a saturation condition, inselected ones of such elements in accordance with such signals bysupplying current to those of the selected ones of such elements whichare in an unsaturated condition and by inhibiting current from beingsupplied to the selected elements which are in the saturation conditionby means disabling each one of the plurality of driver means coupled tosuch remaining ones of the selected elements when the rate of change offlux produced therein reaches a saturation level.

i it i i

1. In a phased array antenna assembly for collimating and directing abeam of electromagnetic energy by actuating, in accordance with controlsignals from a computer, each one of a plurality of magneticallysaturable phase shifters, each one of such phase shifters including atleast one magnetizable element having a first and a second saturationcondition determined by the direction of electric current through anenergizing coil, the improvement comprising: a. separate first andsecond switching means, disposed in circuit between each energizing coiland the computer, for passing electric current through each energizingcoil in a direction determined by a signal from the computer; and b.switching means control circuitry, disposed in operative relationship toeach one of the switching means and responsive to the saturationcondition of the associated magnetizable element when a signal isapplied by the computer, for permitting operation of the switching meansin operative relationship with such element only when the signal fromthe computer commands a change in the saturating condition of themagnetizable element.
 2. In a phased array antenna system wherein anantenna beam is collimated and directed in accordance with beam steeringsignals produced by a computer, the combination comprising: a. aplurality of magnetically saturable phase shifter elements, a portionthereof being in a saturation condition; and b. a plurality of means,each one thereof being coupled to a different one of the plurality ofmagnetically saturable phase shifter elements and responsive to the beamsteering signals to establish a saturation condition in selected ones ofsuch elements by supplying current to the selected ones of suchmagnetically saturable phase shifter elements which are in anunsaturated condition and by inhibiting current from being supplied tothe selected ones of such magnetically saturable phase shifter elementswhich are in the saturation condition, each one of such plurality ofmeans comprising: i. driving means having an input terminal in circuitwith the computer and an output terminal in circuit with one of theplurality of magnetically saturable phase shifter elements, such drivermeaNs being responsive to the beam steering signals to vary the rate ofchange of flux in the magnetically saturable phase shifter element incircuit therewith in accordance with the initial state of the fluxtherein; and ii. disabling means, coupled between the input terminal andthe output terminal, and responsive to the rate of change of flux insuch magnetically saturable phase shifter element to disable the drivingmeans when the rate of change of flux produced therein reaches asaturation level.
 3. In a phased array antenna system wherein an antennabeam is collimated and directed in accordance with beam steering signalsproduced by a computer, the combination comprising: a. a plurality ofmagnetically saturable phase shifter elements; and, b. a plurality ofdriver means, each one thereof being coupled to a different one of theplurality of magnetically saturable elements and having means responsiveto the beam steering signals, to vary the rate of change of flux, andthereby establish a saturation condition, in selected ones of suchelements in accordance with such signals by supplying current to thoseof the selected ones of such elements which are in an unsaturatedcondition and by inhibiting current from being supplied to the selectedelements which are in the saturation condition by means disabling eachone of the plurality of driver means coupled to such remaining ones ofthe selected elements when the rate of change of flux produced thereinreaches a saturation level.